This disclosure relates to a multi-actuator motion control system that minimizes force-fight amongst the actuators.
One example multi-actuator motion control system uses at least two electromechanical actuators (EMAs) that are connected to a synchronization ring. The force outputs of the two actuators are summed to manipulate the position of the synchronization ring, which in turn moves an actuated element. In one example, the position of the synchronization ring is regulated using position sensors integrated into each actuator and in communication with a controller. If the controller considers only the position regulation of the individual EMAs, then errors in position measurement will lead to “force-fight” between the actuators resulting in additional losses and component stress including distortion of the synchronization ring.
The motion of multi-actuator systems can be coordinated by providing the same command vectors to each actuator, resulting in independent controllers that do not compensate each others' behavior. Errors in position measurement or disturbances lead to force-fight between the actuators. In one example master-slave system, one actuator is designated the master, around which the position controller is developed referencing the commanded position. The position controller for the second actuator uses the output (feedback) of the first actuator as its reference. The main drawback to such a system is that a disturbance applied to the second actuator is not reflected to the first actuator. A relative stiffness motion control block can be added to provide feedback to the master controller, resulting in a relative stiffness motion controller coupling the motion response of the two actuators, but force-fight is not addressed.
In another example system, two additional position sensors are used to detect twist along a drive shaft between two actuators. A feedback regulator on one of the actuators is used to eliminate the twist. This arrangement creates a master-slave system using active relative stiffness feedback. The position of the primary system is regulated to the command and the second system is regulated to minimize the twist in the interconnecting drive shaft. Disadvantages of this method include the use of additional sensors to detect the force-fight and that errors between the two actuator sensors command force-fight, which is then compensated by the relative stiffness loop.